In a previous exercise, you observed the flower and its many parts. You were also introduced to the events leading up to double syngamy. The zygote, the product of syngamy of egg and sperm, develops into the embryonic plant. The endosperm, the product of syngamy of the central cell and sperm, accumulates much storage material that is used for the development of the embryonic plant. The embryo and the endosperm reside in integument of the ovule and together these constitute a SEED. Of course the seed is contained within the ovary of the carpel; the gynoecium will develop to form a FRUIT surrounding the seeds. Today you will study the seed and fruit of the flowering plants.

Seed Formation

The integument of the ovule becomes modified to form the SEED COAT. The ENDOSPERM starts developing immediately after double syngamy, forming a parenchymatous tissue inside the ovule and the young embryo. It may store considerable amounts of food material, or it may transfer the food materials to the cotyledon(s) of the embryo and disappear completely. Meanwhile, the zygote undergoes a regular sequence of divisions to form an EMBRYO organized into a central axis (ROOT APEX, RADICLE, HYPOCOTYL, and SHOOT APEX) with appendages (one or two COTYLEDONS). The entire structure--seed coat, storage tissue (endosperm if still present), and embryo--constitutes the SEED and is shed from the parent plant at maturity. The seed usually can withstand quite adverse conditions and remain dormant for considerable periods of time. It serves to disseminate the species.

Observe the demonstration slides of young seeds in Lilium and/or Capsella showing developing endosperm and a young embryo.

In the remaining space, diagram and label a seed of Capsella. Be sure to use the labels printed in BOLD above. Put the seed coat and endosperm labels on the left side of the diagram, and the embryo labels together on the right side of the diagram!

Fruit

The angiosperm seed is derived from the ovule which occurs within the ovary of the carpel. Changes in the ovary wall occur simultaneously with the maturation of the seed, giving rise to a FRUIT. Fruits are of various types--fleshy or dry and, when dry, dehiscent or indehiscent. In some species it may be the fruit with its contained seed(s) which is shed and distributed rather than the seed itself.

Three classifications of some common fruit types is given below. Use this to classify the different fruit types available in the laboratory. Note that a number of common foods are included and that many of these are erroneously classified as "vegetables" when they are actually fruits!

Three Fruit Classification Schemes

1. ORIGINS
   1. Simple fruit - formed from a single pistil (lily, apple, cucumber)
   2. Aggregate fruit - formed from a cluster of separate pistils borne in a single flower (raspberry)
   3. Multiple fruit - formed from the pistils of several to many flowers consolidated with other floral or inflorescence parts (pineapple, fig)
2. COMPOSITION
   1. True fruit - composed of only the ripened ovary, with its contained seeds (lily)
   2. Accessory fruit - composed of the ripened ovary with other additional parts, such as receptacle, bracts, portions of perianth, etc. (apple, cucumber, fig)
3. DESCRIPTIONS
   1. Fleshy Fruits
      1. Drupe - usually 1-seeded, fruit coat with fleshy outer and inner stony layers (peach, plum, olive, raspberry, almond)
      2. Berry - few to many seeded, fruit coat soft and fleshy throughout (grape, banana)
         1. Hesperidium - berry with tough rind (orange, grapefruit)
         2. Pepo - thick-skinned berry, accessory (squash, cucumber)
      3. Pome - fleshy accessory fruit with cartilaginous core (apple, pear)
   2. Dry Fruits
      1. Dehiscent fruits
         1. Follicle - single carpel splitting along one side only (milkweed, magnolia)
         2. Legume - single carpel splitting along both sides (bean)
         3. Capsule - compound pistil, splitting lengthwise or by pores (lily, iris, poppy)
      2. Indehiscent Fruits
         1. Achene - 1-seeded, fruit coat free from seed coat (buttercup, sunflower)
         2. Caryopsis (grain) - 1-seeded, fruit coat fused with seed coat (corn, wheat)
         3. Samara - 1-seeded, fruit with winglike outgrowth (ash)
         4. Nut - 1-seeded, thick hard wall, partially or completely surrounded by cup or husk (oak, filbert)

	Origin	Composition	Description
Raspberry:	aggregate	true	drupe
Apple:	simple	accessory	pome
Mulberry:	multiple	true	drupe

The Peanut

Examine the peanut provided very carefully and dissect it as needed to answer the following:

The Snow Pea Fruit

Examine the snow pea fruit provided very carefully and dissect it as needed to answer the following:

The Cherry Tomato Fruit

Examine the cherry tomato fruit provided very carefully and dissect it as needed to answer the following:

The Strawberry Fruit

Examine the strawberry fruit provided very carefully and dissect it as needed to answer the following:

This page © Ross E. Koning 1994.

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